Piston



Patented Nov. 4, 1941 Application February 24, 1939, Serial No. 258,324In Great Britain September 21, 1938 (Cl. sos- 14) 2 claims.

' This invention relates to pistons primarily for internal combustionengines and has -for its bject to provide a piston which is made mainlyof light alloy and which shall not only have an effective coeicient ofexpansion less than the light alloy itself, but shall also expanduniformly under working conditions. 'I'he two greatest problems met within using pistons of light alloys are:

(I) That the coefficients of expansion of light alloys are greater thanthat of cast-iron and other materials of which cylinders are made, and

(II) That there is always a tendency for the top of a piston skirt toexpand more than'the bottom thereof,

The invention, therefore, seeks to overcome these problems.

In a broad aspect the invention consists in a piston primarily forinternal combustion engines wherein a sheath or sleeve encircling theskirt of the piston and having a coeflicient of expansion less than thatof the skirt is adapted, when the piston expands, to oppose suchexpansion in a radial direction y Thus, according to the invention, asheath or sleeve, of steel for example, may be shrunk or pressed uponthe skirt and the latter may be formed with peripheral grooves intowhich the adjacent'edge of the sheath or sleeve is turned, by spinningfor example, 'to prevent displacement of the sheath, or the sheath orsleeve may be lightly shrunk upon the piston skirt and be 1ocatedthereon by being secured, -as by spot welding, to steel inserts withinapertures inthe piston skirt.

The piston skirt may be formed from a siliconaluminium alloy ofrelatively low expansion coeiiicient and the sheath be of steel, asuitable alloy for the formation of the skirt having the followingcomposition:

Per cent Si1icon 14 Nickel 2 Copper- I 0.9 Magnesium 1 Remainderaluminium. l

This alloy has a coeflicient vof expansion of, approximately, 0.000019C.

'With a piston thus constructed comparatively little stress additionalto the original stress due to the sheath shrinking operation isgenerated on account of heating of the piston under working conditions,while the employment of a steel sheath enables the advantage of analuminium alloy piston, as to light weight, to be retained.

It is -recognised in connection with pistons for internal combustionengines that the top. portion of the skirt tends to expand more than thebottom portion thereof.. The sheath or sleeve provided in accordancewith the invention is provided with the object of resisting thisexpansion, and by making the sheath, which is conveniently of steel,thicker in the region thereof where the lskirt tends to expand more, itis possible to provide that the pistonv shall have an overall equalexpansion. The same object would be achieved n.

'only the skirt of a piston but also the head thereof, so that thesheath extends right up to the edge of the crown of the piston, in whichcase the portion of the sheath in the region of the piston head will bethick enough to permit of the turning of grooves therein for thereception of piston rings in the sheath. It is thus possible to providethe ring grooves in steel instead of in the aluminium of the piston,thereby affording a remedy against wear of the piston ring grooves whichoften gives rise to serious trouble in the case of aluminium oraluminium alloy pistons as employed in internal combustion engines.

The steel sheath may also be made to enclose only the head of thepiston, in which case it is possible to provide ring grooves in steeland at the same time to restrict the expansion of the top part of theskirt, In this case, of course, the lower part of the skirt will expandat the rate normal to the light alloy employed. 'I'he top part of theskirt (which tends to expand more than the bottom), being adjacent tothe steel sheath, will have its expansion to some extent checked by thesheath; and provided the sheath is properly proportioned the result willbe a skirt expanding more or less uniformly at the rate normal to thelight alloy. The object of such modification of the invention is tosecure a piston of uniform expansion affording a remedy against wear ofpiston ring grooves, and lighter than the design mentioned in theimmediately preceding paragraph.

In the accompanying drawing: i

Figures 1 and 2 show in half sectional elevation views of two formswhich the invention may conveniently take.

Figure 1 shows a piston tted with a sheath c encircling the skirt awhich is of reduced diameter in its upper portion so that the sheath iscorrespondingly increased in thickness in its upper portion and may beprovided with grooves d for the piston rings.

Figure 2 shows an adaptation of the invention where the encirclingsheath c may be lightly shrunk upon the piston skirt a and be properlylocated upon the latter by securing the sheath as by spot welding (aspot welded joint being indicated at d) the same to a series of plugs:a`

in and provided with at least one aperture com'- municating with therecess, a metallic sleeve having a coeiiclent of expansion less thanthat of the metal of the piston, a plug fitted tightly within saidaperture, and means securing the plug to the sleeve so that rotarydisplacement of the ysleeve in the recess is prevented.

2. A piston of the type having a metal body j provided with ringreceiving grooves and having a skirt provided with at least one radialaperture therein, a metallic sleeve having a coeiicient of expansionless than that of the metal of the piston, a plug tting within saidaperture and capable of having a sliding movement therein radially ofthe piston body and means securing the plug to the sleeve so that-rotaryand axial displacement of the sleeve is prevented while slight relativeradial movement between the sleeve and the body of the piston ispermitted.

ARTHUR VHLENEUVE MCOLLE.

